The goal of the conducted experiment was to determine the electric current impact on the efficiency of nitrogen compounds oxidation at COD to total Kjeldahl’s nitrogen ratio of 20, 10, 5. The experiments were run in bench scale, in a rotating electro-biological contactor (REBC) under both, conventional conditions (i.e. without electric current) and with electric current passage at the following densities: 0.2 A m⁻², 0.8 A m⁻², and 1.5 A m⁻². The cathode comprised stainless steel discs with immobile biofilm, and the anode a stainless steel electrode, submerged in waste water contained in the flow-tank of the contactor. The process of nitrogen oxidation was the most effective with electric current passage at the density of 1.5 A m⁻² regardless of applied COD/NTK ratio.